Buffer brushes are used in a variety of applications. For example, buffer brushes are used for removing the tread of worn tires. Tire buffing is part of the tire retreading operation. However, buffer brushes used in the process of removing the tread of worn tires often wear out and must be replaced frequently. Buffer brushes are also used to add texture to the surface of a newly manufactured tread.
Typically the tire casing selected for retreading is buffed to remove excess rubber to provide a substantially evenly textured crown for receiving a tread strip and to provide a predetermined tire casing profile. Prior to retreading, the casing must be buffed, generally to a predetermined characteristic crown radius corresponding to the upper contour of the belt package. The casing is buffed to leave only a predetermined thickness of material remaining over the top belt. The shoulder of the casing is also buffed to eliminate or reduce voids or patterns in the shoulder created by the original tread, and to provide a relatively straight profile between the casing side walls and the crown. A worn casing from each of the various models and sizes of new tires has a characteristic tire casing profile of a particular crown width, crown buffing radius and should trim angle which must be created as an initial step in the buffing process.
In present retreading processes, it is important that the surface of the tire casing be carefully buffed about the shoulder areas of the tire to ensure that the tread layer width is approximately the same as the buffed surface of the casing. If the shoulder areas are not sufficiently buffed and trimmed, the tread edges may come loose and/or the cushion gum extending beyond the tread edges will not bond to the casing shoulder. Such problems can reduce the longevity of the retreaded tire and adversely impact the appearance of the retreaded tire.
The tire casing is buffed to remove tread material and to achieve a desired surface texture. Typically, it is desired for the crown and the shoulders of the tire casing to have different textures. The surface texture can be measured on a visual scale propounded by the Rubber Manufacturer's Association (RMA) with a numerical value between 1 and 6 with 1 being the finest and 6 being the roughest texture. Typically, it is desired for the crown of the tire casing to have a RMA number of between 3 and 4 and for the shoulder to have an RMA number of about 2. The shoulders of the tire casing typically are subjected to the largest stresses encountered by the tire during service. The finer texture on the shoulders promotes better adhesion of the tire tread to the casing at these high stresses. If the shoulders received too much texturing, crack propagation in these areas is more likely. In instances where the shoulder receives too little texturing, the bond between the tire casing and the tread is poorer.
The current state of the art in tire casing buffing allows for a multiplicity of tread removal passes, substantially in a sideways, pass after pass method. U.S. Pat. No. 6,745,809 to Mory et al. and assigned to Bandag Licensing Corp. describes a tire buffing apparatus and is incorporated herein in its entirety for everything that it teaches.